I have this ProApp 20S external hard drive for my 1984 Macintosh Plus All-in-One. When I plugged it in and turned it on, it began to smoke profusely after 10 minutes or so. I opened it and noticed it had 4 RIFA capacitors, and at least 1 was blown. I changed all 4, light on the switch goes on...
I've been forwarded to this forum for advice on a Mac Plus All in One I acquired recently. I've been told from the picture of your motherboard, it's definitely a Mac Plus, was likely a 512k once, but it's been upgraded.
When I first tested it it would operate properly for about 5 - 10 minutes...